Desulfurization of hydrocarbon extracts



Patented Nov. 6,. 1951 UNITED STATES PATENT OFFICE DESULFURIZATION OF HYDROCARBON EXTRACTS Frederick William Bertram Porter and Roy Purdy Northeott, Sunbury-on-Thames, England, assignors to Anglo-Iranian Oil'Company Limited, London, England, a British joint-stock corporation No Drawing. Application February 7, 1950, Serial inafter be referred to as aromatic extracts,

although it will be appreciated that they do not consist entirely of aromatic hydrocarbons but inelude varying proportions of other types of hydrocarbons such, for example, as parafiins and naphthenes.

It is known to desulphurise hydrocarbons by passing them with hydrogen over a sulphurresistant hydrogenation catalyst at elevated temperature and elevated pressure, whereby organic sulphur compounds present in the hydrocarbons are hydrogenated to form hydrogen sulphide which can readily be removed from the treated hydrocarbons. The process as normally carried out involves a net consumption of hydrogen, and the cost of supplying the hydrogen is a major factor in the economics of the process. Furthermore, in order to secure the necessary partial pressure of hydrogen it has generally been considered necessary to operate at elevated pressure ranging from 500-1000 lb./sq. in. or more, and a plant to withstand such pressure has to be made from special steels which are relatively expensive. Thus, the usual method for reducing the sulphur content of aromatic extracts, either as such, or blended with other hydrocarbon materials, such as kerosine, is heavy treatment with oleum (up to In the specifications of the co-pending British applications Nos. 17,620/48, 23,583/4'7, 33,120/47, 17,085/48 and 14,834/48, there are described processes for the catalytic desulphurisation of petroleum fractions ranging from light distillates, such as light naphtha, to heavy distillates, such as wax distillates, in which the feedstock is passed to a catalytic desulphurisation zone where it is treated in the presence of a sulphur-resistant hydrogenation catalyst, as specified, under conditions of temperature and pressure such that sufiicient hydrogen is produced by dehydrogenation of naphthene hydrocarbons contained in the feedstock to efiect the conversion of sulphur compounds contained in the feedstock into hydro- In Great Britain December 14,

gen sulphide and to provide a hydrogen-rich gaseous fraction which is recycled to the catalytic desulphurisation zone in order to maintain the necessary partial pressure of hydrogen therein.

It will thus be appreciated that such processes are carried out without the necessity of using extraneous hydrogen and it is convenient to designate such processes as autofining processes, to distinguish them from similar catalytic. .desulphurisation processes carried out with the aid 'of extraneous hydrogen, the latter processes being commonly called hydrofining processes."

The principal object of the present invention is to provide a process whereby aromatic extracts may be desulphurised by conversion of the sulphur contained therein into hydrogen sulphide without the use of hydrogen added from an external source. It is also an object of the invention to enable such a process to be carried out at pressures low enough to avoid the use of special pressure-resisting steels, thereby reducing the cost of the plant. It is a further object of the invention to provide a catalystic desulphurisation process which is efiectivewithout further treat- -ment of the products beyond a light soda wash to remove dissolved hydrogen sulphide.

According to the invention the desulphurisation of an aromatic extract is effected by passing the extract in vapour form in admixture with hydrogen over a catalyst which combines activity for dehydrogenation of naphthenes to aromatics, with activity for the conversion of organically combined sulphur to hydrogen sulphide, and which is not poisoned as a catalyst by the presence of sulphur compounds, at a temperature and pressure sufficient to effect the conversion of a considerable proportion of the sulphur contained in the extract into hydrogen sulphide, and to produce a hydrogen-rich gas mixture which is separated from the treated extract and recycled to the reaction zone at a rate sufficient to maintain the necessary partial pressure of hydrogen therein.

The invention may be applied to aromatic extracts as such, or in the form of blends with other hydrocarbon fractions, such as tractors vapourising oil which consists of a blend of aromatic extract and kerosine;

It is believed that the reaction proceeds by dehydrogenation of some of the naphthenes present Q,

extent on the sulphur content, and the higher the V sulphur content, the higher the temperature necessary to provide suflicient hydrogen. At temperatures above about 800 F. the on-stream time is reduced. The preferred temperature of operation is also to some extent dependent upon the pressure employed which is preferably between 50 and 250 lb./sq. in. As the pressure is increased, the minimum temperature at which satisfactory dehydrogenation of the naphthenes can be obtained increases, and if at a fixed temperature the pressure is sufficiently increased, the reverse reaction of hydrogenation of aromatics begins to occur. Thus, when operating at the higher pressures it is preferable to use higher temperatures. Similarly, it is desirable to avoid the combination of high temperature and low pressure since such conditions lead to a short on-stream time for satisfactory operation.

The space velocity may be varied according to the degree of desulphurisation required and the activity of the catalyst, but space velocities above 10 v./v./hr. result in a low degree of desulphurisation.

Among the catalysts that may be used are metal sulphides and oxides especially those of the 6th group either alone (for example chromium oxide and tungsten sulphide) or in admixture with other sulphides or oxides (for example pellets consisting of two parts tungsten sulphide and one part nickel sulphide) or in combination with other oxides or sulphides (for example cobalt molybdate or thiomolybdate) or mixed with or deposited on a porous support such as natural or processed bauxite, activated alumina and kieselguhr. Natural and processed bauxites may themselves be used as catalysts. The preferred catalyst, however, consists of cobalt molybdate supported on alumina.

An effective pelleted catalyst was prepared by mixing powdered cobalt oxide, molybdenum oxide and alumina, and pelleting with 1% graphite into pellets which were then treated for two hours at 550 C. The catalyst may also be prepared by extrusion.

An effective supported molybdate catalyst was prepared by the impregnation of roasted Indian bauxite with a cobalt molybdate solution so that the molybdenum content of the material stable at 1000 F. was 3.6% by weight while the cobalt content of the material stable at 1000 F. was 1.0% weight.

The autofining process may be operated by setting the pressure in the autofining zone at a predetermined level and thereafter withdrawing from the system gas in excess of that required to maintain the predetermined pressure. In this case, there is a continuous make of hydrogen indicating that the hydrogen produced in the dehydrogenation reaction is not being fully utilised in the desulphurisation reaction. An improved method of operation was therefore developed in which the hydrogen-containing gaseous fraction is recycled to the reaction zone and the pressure therein allowed to rise to an equilibrium pressure at which the hydrogen evolved equals the hydrogen consumed. This method of operation is fully described in the specification of the co-pending No. 9,672/49 and results in a greater degree of desulphurisation and increased on-stream hours for a product of given sulphur content.

The preferred catalyst for use in the autofining process is of the so-called cobalt molybdate type which consists of the oxides of cobalt and molybdenum deposited on or incorporated with a support, preferably alumina. It has been found that there is a period at the commencement of each run during which the gas make is negligible or non-existent and the desulphurisation is not at its maximum. This low dehydrogenating activity of the catalyst is more noticeable at low feedstock velocities and with the heavier feedstocks. It was discovered that the inactivity of the catalyst during the early hours on-stream could be largely overcome by subjecting the cobalt molybdate catalyst to the'action of hydrogen sulphide or hydrogen sulphide-containing gases prior to its use in the autofining process. An autofining process using such a catalyst is described in the specification of the co-pending application No. 24,330/49.

The following are examples of the process of the invention.

EXAMPLE 1 An S02 extract of Iranian origin having a sulphur content of 0.69% weight was passed at a temperature of 780 F. and a pressure of 100 lb./sq. in. over a catalyst consisting of cobalt molybdate supported on alumina. The space velocity was maintained at 2 v./v./hr. and the process was continued satisfactorily for a period of 100 hours during which time there was an average gas make of 15 cu. ft./bbl. This gas contained by volume of hydrogen and was recycled to the reaction zone at a rate of 2000 cu. ft./bbl.

The product represented 99% weight on feed and the inspection data of the feedstock and product are set out in the following table, No. 1.

It will be seen that a product containing 0.05% weight sulphur was obtained from an extract containing 0.69% weight sulphur, representing a sulphur removal of 93.5%. Except for a light soda wash to remove dissolved hydrogen sulphide, no further treatment of the product was required.

EXAMPLE 2 A mixture of 45% by volume of S02 extract of Iranian origin having a sulphur content of 0.9% wt., and 55% by volume of kerosine of Iranian origin boiling between 160 C. and 260 C., the mixture having a total sulphur content of 0.55% wt., was passed at a temperature of 780 F. and a pressure of lb./sq. in. over a catalyst consisting oi cobalt molybdate. supported on. alumina.

The space velocity was maintained at 5.0 v./v./hr. and theprocess was continued satisfactorily for a period of 200 hours during which time there was an average gas make of' 20 cu. ft./bbl. This gas contained 85% by volume of hydrogen and was recycled to the reaction zone at the rate of 2000 cu. ft./bbl.

The product represented 99% weight on feed and the inspection data of the feedstock and product are set out in the following table, N0. 2.

TABLE 2 Inspection Data Feedstock Product EXAMPLE 3 This example illustrates the application of the equilibrium pressure method of operation which is described in the specification of the co-pending application No. 9,672/49.

The feedstock was a crude kerosine S02 extract prepared from mixed Iranian and Iraqi crudes of boiling range 161 to 288.5 C. (A. S. T. M.).

Autofining conditions Catalyst, cobalt molybdate on alumina Temperature (average), 800 F. Pressure, equilibrium (100-68 p. s. 1. ga.) Space velocity, 3.0 v./v./hr. Recycle rate, 2000 c. f./b. (at 1000 p. s. 1. ga.) Duration of run, 1'74 hrs.

Inspection Data 3 2 3 3;

s. (3., 60 0.8675 0. 8630 I. B. P. 161 155 7 vol. 171 170 50% Vol. 190 191 90% vol. 241 235 F. B. P., 288.5 279 Bromine No. 3 6 Octane No. (M M) 76.8 79.2 Sulphur, 1. 0o 0. 36 Sulphur Removal, 64.0

EXAMPLE 4 The feedstock was a benzine S02 extract of 115 to 162.5 C. A. S. T. M. boiling range containing approximately '75 per cent aromatics prepared from mixed Iranian crudes.

Autofining conditions Catalyst, cobalt molybdate on alumina Temperature, 780 F.

Pressure, 100 p. s. i. ga.

Space velocity, 3.0 v./v./hr.

Recycle rate, 2000 c. f./b.

Duration of run, 60 hours.

Average gas make, 5 c. f./b.

Feed- Bulked Inspection Data Stock Product 0. 836 0. 835 115 110 120 119 129 127 145 144 162. 5 164 2 1 +15 +21 1 1 l l Octane N o. (M. M.) 85.3 87. 2 Sulphur, per cent wt 0.295 0. 004 Sulphur Removal, per cent- 98. 6

EXAMPLE 5 Feedstock components 45% vol. Iranian/Iraqi kerosine S02 extract, 163

to 293 C. A. S. T. M. vol. Iranian/Iraqi kerosine, 162 to 301 C.

A. S. T. M. 20% vol. Iranian/Iraqi naphtha, 143 to 184 C.

A. S. T. M-

Autofining conditions Catalyst, cobalt molybdate on alumina Temperature, 780 F.

Pressure, 100 p. s. i. ga.

Space velocity, 3.0 v./v./hr.

Recycle rate, 2000 c.f./b.

Duration of run, 422 hours Average gas make, 2.5 c.f./b.

Inspection Data Feed- Bulked 35 stock Product S. G. 60 F./60 F 0. 824 0. 821 IJB. P., 'C 151 149 10% v01. C 164. 5 164 50% vol. 0. 185 186 90% vol. C. 243 243.5 F. B. P. o--- 292 283.5 Colour, Saybolt 6 9 Sulphur, per cent wt 0. 577 0. 126 Sulphur Removal, per cent... 78 Octance No. (M. M.) 48. 1 51. 2

EXAMPLE 6 The feedstock was a 50-90% vol. tray cut from a kerosine S02 extract prepared from Iraqi crude and had a boiling range of 18'7252 C. A. S. T. M.

Autofining conditions Catalyst, cobalt molybdate on alumina Temperature, 780 F.

Pressure, p. s. i. ga.

Space velocity, 1.6 v./v./hr.

Recycle rate, 3400-4400 c.f./b. Duration of run, 300 hours Bulked Inspection Data Product Sulphur, per cent wt Sulphur Removal We claim:

1. A process for the hydrocatalytic desulphurization of a sulphur-and-naphthene-containing aromatic extract of hydrocarbon oil, which process is self-supporting with respect to the hydrogen needed and is productive of a desulphurized aromatic extract having, except for lowered sulphur content, properties and boiling range substantially the same as the feedstock, comprising the steps of passing a feedstock consisting of the aromatic extract to be desulphurized to a reaction zone and contacting the feedstock therein with a dehydrogenation-hydrogenation catalyst and with hydrogen derived solely from the feedstock, said catalyst being resistant to sulphur poisoning and combining activity for the dehydrogenation of naphthenes in said feedstock to aromatics with activity for the hydrogenation of organically combined sulphur in said feedstock to hydrogen sulphide; maintaining a selected temperature in said zone between about 700 F. to about 800 F. at which hydrogen is continuously produced from said feedstock; maintaining a selected pressure in said zone between about 50 to about 250 lbs./sq. in. gauge, said selected temperature and pressure being correlated to provide, from the dehydrogenation of naphthenes contained in said feedstock, a net production of hydrogen at least sufficient to convert organically combined sulphur in the feed stock into hydrogen sulphide and to maintain said selected pressure; separating hydrogen sulphide and a hydrogen-rich gas mixture from the desulphurized feedstock; recycling said hydrogen-rich gas mixture to the reaction zone to constitute the whole of the. hydrogen supplied to said zone, the hydrogen recycle rate being sufficient to maintain the necessary partial pressure of hydrogen in said zone; and, recovering the desired desulphurized aromatic extract from the residue of said separating operation.

2. A process according to claim 1, wherein the feedstock is passed to said reaction zone at a.

space velocity less than about 10 v./v./hr., wherein the selected temperature is approximately 780 F., wherein the selected pressure is approximately lbs/sq. in. gauge, and wherein said hydrogen-rich gas mixture is recycled in the reaction zone at a rate between about 2000 and 4000 cu. ft./bbl. of feedstock.

3. A process according to claim 1, wherein the catalyst consists of the combined oxides of cobalt and molybdenum supported on alumina.

4. A process according to claim 1, wherein the feedstock consists of a blend of aromatic extract and kerosene.

5. A process according to claim 1, wherein the feedstock consists of a blend of an aromatic kerosene extract, a kerosene fraction, and a naphtha fraction.

FREDERICK WILLIAM BERTRAM PORTER. ROY PURDY NORTHCOT'I.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Byrns et al., Ind. and Eng, 35, No. 11, pages 1160-1167. 

1. A PROCESS FOR THE HYDROCATALYTIC DESULPHURIZATION OF A SULPHUR-AND-NAPHTHENE-CONTAINING AROMATIC EXTRACT OF HYDROCARBON OIL, WHICH PROCESS IS SELF-SUPPORTING WITH RESPECT TO THE HYDROGEN NEEDED AND IS PRODUCTIVE OF A DESULPHURIZED AROMATIC EXTRACT HAVING, EXCEPT FOR LOWERED SULPHUR CONTENT, PROPERTIES AND BOILING RANGE SUBSTANTIALLY THE SAME AS THE FEEDSTOCK, COMPRISING THE STEPS OF: PASSING A FEEDSTOCK CONSISTING OF THE AROMATIC EXTRACT TO BE DESULPHURIZED TO A REACTION ZONE AND CONTACTING THE FEEDSTOCK THEREIN WITH A DEHYDROGENATION-HYDROGENATION CATALYST AND WITH HYDROGEN DERIVED SOLELY FROM THE FEEDSTOCK SAID CATALYST BEING RESISTANT TO SULPHUR POISONING AND COMBINING ACTIVITY FOR THE DEHYDROGENATION OF NAPHTHENES IN SAID FEEDSTOCK TO AROMATICS WITH ACTIVITY FOR THE HYDROGENATION OF ORGANICALLY COMBINED SULPHUR IN SAID FEEDSTOCK TO HYDROGEN SULPHIDE; MAINTAINING A SELECTED TEMPERATURE IN SAID ZONE BETWEEN ABOUT 700* F. TO ABOUT 800* F. AT WHICH HYDROGEN IS CONTINUOUSLY PRODUCED FROM SAID FEEDSTOCK; MAINTAINING A SELECTED PRESSURE IN SAID ZONE BETWEEN ABOUT 50 TO ABOUT 250 LBS./SQ. IN. GAUGE, SAID SELECTED TEMPERATURE AND PRESSURE BEING CORRELATED TO PROVIDE, FROM THE DEHYDROGENATION OF NAPHTHENES CONTAINED IN SAID FEEDSTOCK, A NET PRODUCTION OF HYDROGEN AT LEAST SUFFICIENT TO CONVERT ORGANICALLY COMBINED SULPHUR IN THE FEEDSTOCK INTO HYDROGEN SULPHIDE AND TO MAINTAIN SAID SELECTED PRESSURE; SEPARATING HYDROGEN SULPHIDE AND A HYDROGEN-RICH GAS MIXTURE FROM THE DESULPHURIZED FEEDSTOCK; RECYCLING SAID HYDROGEN-RICH GAS MIXTURE TO THE REACTION ZONE TO CONSTITUTE THE WHOLE OF THE HYDROGEN SUPPLIED TO SAID ZONE, THE HYDROGEN RECYCLE RATE BEING SUFFICIENT TO MAINTAIN THE NECESSARY PARTIAL PRESSURE OF HYDROGEN IN SAID ZONE; AND, RECOVERING THE DESIRED DESULPHURIZED AROMATIC EXTRACT FROM THE RESIDUE OF SAID SEPARATING OPERATION. 